FACTORS INFLUENCING THE CONCENTRATION OF GAS-PHASE HYDROGEN-PEROXIDE DURING THE SUMMER AT KINTERBISH, ALABAMA

Measurements of H2O2 along with a variety of other photochemically act ive compounds were made during the summers of 1990 and 1992 at a rural site in Alabama. The chemical composition in the air sampled at this site provides an interesting contrast to earlier measurements made at a site in the Colorado mountains. Even though the ozone levels were sl ightly smaller, the H2O2 levels were a factor of 2 to 3 higher at the Alabama site. These measurements serve to further test our understandi ng of the meteorological and chemical parameters that determine the co ncentration of H2O2 in the rural troposphere. Deposition beneath a sha llow nocturnal inversion layer as well as precipitation events played a major role in the loss of H2O2 and had a strong effect on the diurna l trend When these major influences were eliminated through selection of dry, high sunlight and midmorning to late afternoon periods only, s everal relationships were apparent. A strong positive correlation betw een H2O2 and temperature was probably due to an increase in the concen tration of isoprene with temperature. Isoprene serves as a major sourc e of HO2 radicals, the precursors of H2O2. At the Alabama site, higher temperatures lead to much higher isoprene levels and, consequently, t he higher H2O2 levels compared to the Colorado site. At the Alabama si te the relative humidity was anticorrelated with the concentration of H2O2, probably due to the effect of the humidity on deposition, eviden tly the dominant loss process. H2O2 exhibited only a weak positive cor relation with O-3 and no correlation with H2O. The degree of photochem ical processing of the air mass was positively related to the concentr ation of H2O2. An increase in the concentration of NOx had a small but significant negative effect on the level of H2O2, and the diurnal cor relation of H2O2 closely reflected the variation of the ratio of the c oncentrations of isoprene to NOx, which again reflects the important r ole isoprene may play as a photochemical precursor for H2O2 and the in verse role that NOx plays in curtailing the photochemical production o f H2O2. Finally, the H2O2 to HNO3 ratio indicates that the photochemis try is strongly NOx limited at this Alabama site.